The present invention relates to the separation of copper from nickeliferous sulfidic materials and, more particularly, to a pyrometallurgical process for separating copper from nickeliferous sulfidic ores, ore concentrates, mattes, or other metallurgical intermediates.
Copper is nearly always co-present in nickeliferous sulfide ores and nickel is frequently present in minor amounts in cuperiferous sulfidic ores. The cuperiferous and nickeliferous pyrrhotitic ores found in the northern United States, Canada, southern Africa and the USSR are examples of such ores in which copper and nickel are co-present.
After being mined, sulfidic ores are commonly crushed, ground and subjected to a bulk flotation treatment to separate the gangue from the mineral values. Typically, bulk concentrates can contain between about 5% and about 20% copper and between about 2% and about 10% nickel with the two metals being present in a wide range of ratios. The separation of copper from nickel in these concentrates has been the focus of extractive metallurgists over the years.
Copper and nickel values contained in pyrrhotitic ore concentrates have been separated in any one of a number of ways. All these processes, however, begin with the smelting of the concentrate, either in a blast furnace or in a reverbatory furnace. The literature contains many references to processes actually used to separate copper and nickel values contained in matte produced by matte smelting. All these methods are described in considerable detail, for example, in the book "The Winning of Nickel" by J. R. Boldt, Jr., VanNostrand, New York, 1967.
Both pyrometallurgical and hydrometallurgical approaches have been used. Among the former group is the old (and now obsolete) Orford process in which the copper-nickel conversion matte obtained after iron removal by slagging is smelted with sodium sulfide to generate a sodium copper sulfide liquid phase that is immiscible in liquid nickel sulfide and forms a top sodium-copper sulfide liquid layer. After solidification, the two layers are mechanically separated and individually treated for recovery of copper and nickel.
Another pyrometallurgical method involves controlled slow cooling of the matte which promotes the formation of discreet particles of nickel sulfide, copper sulfide and a metallic fraction within the slowly cooled matte. These products are then recovered by a combination of crushing, grinding, flotation and magnetic separation.
Still another pyrometallurgical method of separating nickel and copper in converter matte (especially where the nickel to copper ratio is low) is to overblow the matte beyond the point of iron removal. Nickel is preferentially oxidized by this treatment and the comparatively low chemical potential of nickel in the overlying slag results in the selective removal of nickel values from the copper phase into the slag phase. If nickel recovery is intended, this slag must be subsequently treated, as by leaching or by energetic electric furnace reduction processing.
Hydrometallurgy applied to copper-nickel matte is also commercially used for separating copper and nickel in these materials. Nickel values can be recovered separately from the matte by controlled oxidative leaching, or copper can be recovered by roasting the matte and leaching with acid whereby copper values are selectively dissolved from the roasted matte.
As is clearly evident from the above, none of the conventional practices has to this time succeeded in providing an economical, simple process for separating nickel and copper combined in complex copper-nickel ores prior to the point where the concentrate containing copper and nickel has been smelted to a matte. This entails some significant disadvantages. The further pyrometallurgical treatment of matte beyond the smelting stage produces secondary sources of sulfur dioxide including fugitive emissions. These are known to be costly, if not impossible, to control. The hydrometallurgical treatment of mattes can also involve a secondary sulfur disposal problem if the matte is roasted prior to leaching. If matte is not roasted prior to leaching, that is, if it is leached directly, the further separation of the sulfides involves a complicated series of selective leaching steps that are, at the very least, expensive to carry out and require a high degree of control.